A report issued by IPCC (Intergovernmental Panel on Climate Change) in 2007 shows that it is highly reliable (9 out of 10 are correct) that global warming is caused by greenhouse gases emitted through human activities. At present, this report is most accepted across the world. Further, this report shows that it is essential to promptly make a greater effort, by which importance of struggling against the global warming has been socially recognized.
Under these circumstances, various countermeasures have been taken under the government initiative. One of the countermeasures is to encourage the use of power generated by natural energy such as wind power and sunlight. The natural energy cannot be stably supplied, and thus the stability of a power system connected to the natural energy is affected. Accordingly, a power storage (storage battery) is used as a buffer for stabilizing the unstable supply from the energy source.
It is assumed that an expensive appliance such as storage battery is introduced to be shared among a plurality of members. In most of conventional methods concerning a system for sharing a storage battery, efficient utilization of the storage battery is a main object, and it is not often that cost burden is focused on. In a system based on a conventional method, the cost burden of a storage battery to be shared is determined depending on the amount of used power and occupancy time of the appliance. However, when a plurality of members utilize and share a facility or an appliance suffering remarkable deterioration as in the storage battery, the facility cost is unfairly shared since deteriorating influence on the appliance is not considered depending on the utilization situation of each member.